iommu/mediatek: Remove unused "mapping" member from mtk_iommu_data

Just remove a unused variable that only is for mtk_iommu_v1.

Signed-off-by: Yong Wu <yong.wu@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Link: https://lore.kernel.org/r/20221018024258.19073-7-yong.wu@mediatek.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>